A technique has been known in which: cameras installed in a vehicle capture and obtain images of surroundings of the vehicle; and an amount of movement of the vehicle is obtained based on changes in the images (see Japanese Patent Application Publication No. 2008-175717). Japanese Patent Application Publication No. 2008-175717 aims at obtaining the amount of movement of the vehicle accurately even if the vehicle moves slightly at slow-speed. To this end, a feature point is detected from each image; the position of the feature point is obtained; and thereby, the amount of movement of the vehicle is obtained from the direction and distance of movement (amount of movement) of the feature point.
In addition, a technique of performing a three-dimensional measurement using a laser beam projector for projecting a laser beam in a grid pattern (patterned light beam) has been known (see Japanese Patent Application Publication No. 2007-278951). According to Japanese Patent Application Publication No. 2007-278951, an image of an area of the projected patterned light beam is captured with a camera; the patterned light beam is extracted from the captured image; and a behavior of the vehicle is obtained from the position of the patterned light beam.
In a case where, however, using the technique described in Japanese Patent Application Publication No. 2008-175717 to detect feature points on the road surface in the same area as the area of the projected patterned light beam described in Japanese Patent Application Publication No. 2007-278951, it is difficult to distinguish between the patterned light beam and the feature points. On the other hand, in a case where feature points on the road surface are detected in an area away from the area of the projected patterned light beam, an error in calculating amounts of movements of the feature points becomes larger.